Batteries are commonly used as electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized. The cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material.
When a battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide the electrical power. The electrolyte in contact with both anode and cathode contains ions that flow through the separator between anode and cathode to maintain charge balance throughout the battery during charge and discharge.
A primary goal in designing a battery is long service life. Long service life really means the battery can provide high energy throughput. But high energy throughput is dependent on the battery discharge capacity, the electrode voltage as well as the number of cycles that the battery can be discharged.
The primary advantage of Nickel-Iron battery is high in cycle life. This means that the battery can be charged and discharged many times. The chief disadvantage of Nickel-Iron battery is, however, the poor rate capability because of the inherently low discharge voltage of the iron electrode. Low discharge voltage to a given end of discharge voltage cut off has resulted in low discharge capacity for the Nickel-Iron battery. Because the dischargeable capacity under a given load per cycle is determined by the length of time for the discharging battery to reach a predetermined cut off voltage at which the battery is no longer useful for its intended purpose.
Therefore, the energy throughput of Nickel-Iron battery can still be low even though its cycle life is known to be high. Any means to increase the discharge voltage of iron electrode to increase discharge capacity and energy throughput would bring significant commercial interest.
A common sense approach to increase energy throughput has been to increase the interior volume of the battery to allow for more active materials within the cell. More active material would surely bring longer discharge capacity and higher voltage due to lower current density on the iron anode, but increasing battery size also means lower energy density and higher cost.
A more beneficial approach to increase battery capacity to a given cut off voltage without resorting to the use of additional active material is employing an electro-conductive additive to enhance the discharge kinetic iron oxide anode. Therefore, the discharge voltage of iron oxide anode can be raised without resorting the use of additional iron oxide active material. The benefits of electro-conductive additive include higher battery energy density and higher energy throughput for Nickel-Iron battery.